All drawings appearing in this Recommendation have been done in Autocad.

Recommendation E.8001)

QUALITY OF SERVICE AND DEPENDABILITY VOCABULARY

CONTENTS

1	Introduction

2	Related Recommendations

3	Performances

3.1	Service related performances

3.2	Item related performances

4	Interruptions

5	Measures of performances

5.1	Service support performance

5.2	Service operability performance

5.3	Service accessibility performance

5.4	Service retainability performance

5.5	Serveability performance

5.6	Transmission performance

6	Common concepts

Annex A - Alphabetical list of definitions contained in this Recommendation

1	Introduction2)

A consistent set of terms and definitions is necessary for the development of Recommendations in the important areas of quality of service and network performance by the numerous Study Groups responsible for the

Recommendations. Terminology standardization is also necessary to align the work of the various groups and to avoid confusing the users of Recommendations by the introduction of conflicting terms and definitions. Therefore, this Recommendation sets forth a simple set of terms and definitions relating to the concept of the quality of telecommunications services and network performance. These terms and definitions apply to all telecommunications services and all network arrangements used to provide the services.

The diagram in Figure 1/E.800 is intended to provide an overview of the factors which contribute collectively to the overall quality of service as perceived by the user of a telecommunication service. The terms in the diagram can be thought of as generally applying either to the quality of service levels actually achieved in practice, to objectives which represent quality of service goals to be achieved, or to requirements which reflect design specifications.

The diagram in Figure 1/E.800 is also structured to show that one quality of service factor can depend on a number of others. It is important to note

- although it is not explicitly stated in each of the definitions to follow - that the value of a characteristic measure of a particular factor may depend directly on corresponding values of other factors which contribute to it. This necessitates, whenever the value of a measure is given, that all of the conditions having an impact on that value be clearly stated.

An essential aspect of the global evaluation of a service is the opinion of the users of the service. The result of this evaluation expresses the users' degrees of satisfaction. This Recommendation establishes:

1)	a general framework for the quality of service concept

2)	the relationship between quality of service and network performance

3)	a set of measures for these performances.

It is obvious that a service can be used only if it is provided, and it is desirable that the provider have a detailed knowledge about the quality of the offered service. From the provider's viewpoint, network performance is a concept by which network characteristics can be defined, measured and controlled to achieve a satisfactory level of service quality. The interests and the viewpoints of users and providers are different, and usually require a compromise between quality and economics.

In the utilization of a service the user identifies two ½bodies :

1)	the "Organization(s)", i.e., the telecommunication Administration, operating company, etc. providing the means and facilities for the access to and the utilization of the service;

2)	the ½network , i.e., the necessary means (terminals3), lines, switches, etc.) actually used.

The contribution of the Organization to the quality of service is characterized by one performance concept, service support performance, as shown in Figure 1/E.800.

The contribution of the network to the quality of service is characterized by three performance concepts, which are:

-	service operability performance, i.e., the ease by which the service can be used, including the characteristics of terminal equipment, the intelligibility of tones and messages, etc.;

-	serveability performance, the ability of a service to be obtained - within specified tolerances and other given conditions - when requested by the user and continue to be provided for the requested duration. Thus, serveability performance describes the response of the network during the establishment, retention and release of a service connection;

-	service integrity, the degree to which a service is provided without excessive impairments, once obtained. Thus, service integrity is primarily concerned with the level of reproduction of the transmitted signal at the receiving end.

The serveability performance is further subdivided into two terms:

-	service accessibility performance, the ability of a service to be obtained - within specified tolerances and other given conditions - when requested by the user, further subdivided into (1) network accessibility, which is the ability of the user to obtain access to the network for a service request, and (2) connection accessibility, which is the ability of the network to provide the user with a satisfactory connection to the intended destination;

-	service retainability performance, which is the ability of the service, once obtained, to continue to be provided under given conditions for a requested period of time. That is, service retainability performance covers the proper retention of connections and the release (disengagement) when requested by the user.

Serveability performance is divided into trafficability performance, dependability and propagation performance as shown in Figure 1/E.800. The trafficability performance is described in purely teletraffic engineering terms (see Recommendation E.600). The measures are expressed in terms of losses and delay times. Dependability is the combined aspects of availability, reliability, maintainability and maintenance support performances and relates to the ability of an item to be in a state to perform a required function (see Supplement No. 6). Propagation performance refers to the ability of the transmitting medium to transmit the signal within intended tolerances.

Figure 1/E.800 - CCITT 31424

Measures for all of the above performances may be related to an instant of time (instantaneous, etc.) or expressed as a mean value over a time interval. These and other recommended qualifiers (measure modifiers) are found in Supplement No. 6.

Supplement No. 6 further provides recommended statistical terms and definitions for use in the application of measures related to all performances.

While dependability is used only for a general description in non-quantitative terms, the actual quantification is done under the heading of availability performance, reliability performance, maintainability performance and maintenance support performance.

The most important of these dependability-related measures are found in Supplement No. 6, Part I. The properties expressed by these measures impact the measures related to quality of service and network performance and are thus implicitly characterizations of these performances.

Measures are connected to events (failure, restoration, etc.), states (fault, up state, down state, outage, etc.) or activities (e.g. maintenance), with their time durations.

Part I of Supplement No. 6 provides necessary identification of times, events, states and maintenance activities.

2	Related Recommendations and Supplements

Recommendation E.600:	Terms and definitions of traffic engineering

Supplement No. 6:	Terms and definitions for quality of service, network performance, dependability and trafficability studies.

3	Performances

3.1	Service related performances

3101	quality of service

F	qualité de service

S:	calidad de servicio

The collective effect of service performances which determine the degree of satisfaction of a user of the service.

Note 1 - The quality of service is characterized by the combined aspects of service support performance, service operability performance, serveability performance, service integrity and other factors specific to each service.

Note 2 - The term "quality of service" is not used to express a degree of excellence in a comparative sense nor is it used in a quantitative sense

for technical evaluations. In these cases a qualifying adjective (modifier) shall be used.

3102	serveability performance

F:	servibilité (d'un service)

S:	servibilidad (de un servicio)

The ability of a service to be obtained - within specified tolerances and other given conditions - when requested by the user and continue to be provided for a requested duration.

Note - Serveability performance may be subdivided into the service accessibility performance and the service retainability performance.

3103	service accessibility performance

F:	accessibilité (d'un service)

S:	accesibilidad (de un servicio)

The ability of a service to be obtained, within specified tolerances and other given conditions, when requested by the user.

Note - This takes into account the transmission tolerance and the combined aspects of propagation performance, trafficability performance and availability performance of the related systems.

3104	service retainability performance

F:	continuabilité (d'un service)

S:	retenibilidad (de un servicio)

The ability of a service, once obtained, to continue to be provided under given conditions for a requested duration.

Note - Generally this depends on the transmission tolerances, the propagation performance and reliability performance of the related systems. For some services, for example packet switching, this also depends on the trafficability performance and the availability performance of the related systems.

3105	service support performance

F:	logistique de service

S:	logística del servicio

The ability of an organization to provide a service and assist in its utilization.

Note - An example of service support performance is the ability to provide assistance in commissioning a basic service, or a supplementary service such as the call waiting service or directory enquiries service.

3106	service operability performance

F:	facilité d'utilisation (d'un service)

S:	facilidad de utilización (de un servicio)

The ability of a service to be successfully and easily operated by a user.

3107	service integrity

F:	integrité de service

S:	integridad del servicio

The degree to which a service is provided without excessive impairments, once obtained.

Note - This service is characterized by the transmission performance of the system.

3108	transmission performance

F:	qualité de transmission

S:	calidad de transmisión

The level of reproduction of a signal offered to a telecommunications system, under given conditions, when this system is in an up state.

3.2	Item related performances

3201	network performance

F:	qualité technique du réseau

S:	calidad de funcionamiento de la red

The ability of a network or network portion to provide the functions related to communications between users.

Note 1 - Network performance contributes to serveability performance and service integrity (see Figure 2/E.800).

Note 2 - Network performance measures are meaningful to network providers and are quantifiable at boundaries of network portions to which they apply. Quality of service measures are only quantifiable at a service access point.

Figure 2/E.800 - T0201420-88

3202	trafficability performance

F:	traficabilité; capacité d'écoulement du trafic

S:	aptitud para cursar tráfico

The ability of an item to meet a traffic demand of a given size and other characteristics, under given internal conditions.

Note - Given internal conditions refer, for example, to any combination of faulty and not faulty sub-items.

3203	capability

F:	capacité; capabilité (d'une entité)

S:	capacidad

The ability of an item to meet a demand of a given size under given internal conditions.

Note 1 - Internal conditions refer, for example, to any given combination of faulty and not faulty sub-items.

Note 2 - This is also called trafficability performance.

3204	propagation performance

F:	caractéristiques de propagation

S:	característica de propagación

The ability of a propagation medium, in which a wave propagates without artificial guide, to transmit a signal within the given tolerances.

Note - The given tolerances may apply to variations in signal level, noise, interference levels, etc.

3205	effectiveness (performance)

F:	efficacité

S:	efectividad

The ability of an item to meet a service demand of a given size.

Note - This ability depends on the combined aspects of the capability and the availability performance of the item.

4	Interruptions

4101	interruption; break (of service)

F:	interruption; coupure (d'un service)

S:	interrupción (de un servicio); corte (de un servicio)

Temporary inability of a service to be provided persisting for more than a given time duration, characterized by a change beyond given limits in at least one parameter essential for the service.

Note 1 - An interruption of a service may be caused by disabled states of the items used for the service or by external reasons such as high service demand.

Note 2 - An interruption of a service is generally an interruption of the transmission, which may be characterized by an abnormal value of power level, noise level, signal distortion, error rate, etc.

4102	time between interruptions

F:	temps entre interruptions

S:	tiempo entre interrupciones

The time duration between the end of one interruption and the beginning of the next.

4103	interruption duration

F:	durée d'interruption

S:	duración de interrupción

The time duration of an interruption.

4104	mean time between interruptions (MTBI)

F:	durée moyenne entre interruptions (DMEI)

S:	tiempo medio entre interrupciones

The expectation of the time between interruptions.

4105	mean interruption duration (MID)

F:	durée moyenne d'une interruption (DMI)

S:	duración media de una interrupción

The expectation of the interruption duration.

5	Measures of performances

5.1	Service support performance

5101	mean service provisioning time

F:	délai moyen pour la fourniture d'un service

S:	tiempo medio de espera (para la prestación de un servicio)

The expectation of the duration between the instant of time a potential user requests that an organization provides the necessary means for a service, and the instant of time when these means are furnished.

5102	billing error probability

F:	probabilité d'erreur de facturation

S:	probabilidad de error de facturación

The probability of an error when billing a user of a service.

5103	incorrect charging or accounting probability

F:	probabilité de taxation erronée

S:	probabilidad de tarificación o de contabilidad incorrectas

The probability of a call attempt receiving incorrect charging or accounting treatment.

5104	undercharging probability

F:	probabilité de sous-taxation

S:	probabilidad de subtarificación

The probability that an effective call will be undercharged for any reason.

5105	overcharging probability

F:	probabilité de surtaxation

S:	probabilidad de sobretarificación

The probability that an effective call will be overcharged for any reason.

5106	billing integrity (probability)

F:	(probabilité de) justesse de facturation

S:	integridad de la facturación (probabilidad de)

The probability that the billing information presented to a user correctly reflects the type, destination and duration of the call.

5.2	Service operability performance

5201	service user mistake probability

F:	probabilité d'erreur d'un usager

S:	probabilidad de error de un usuario (de un servicio)

Probability of a mistake made by a user in his attempt to utilize a service.

5202	dialling mistake probability

F:	probabilité d'erreur de numérotation

S:	probabilidad de error de marcación

The probability that the user of a telecommunication network makes dialling mistakes during his call attempts.

5203	service user abandonment probability

F:	probabilité d'abandon (d'accès à un service par un usager)

S:	probabilidad de abandono de un servicio por un usuario

The probability that a user abandons the attempt to use a service.

Note - Abandonments may be caused by excessive user mistake rates, by excessive service access delays, etc.

5204	call abandonment probability

F:	probabilité d'abandon (d'une tentative d'appel)

S:	probabilidad de abandono de una tentativa de llamada

The probability that a user abandons the call attempt to a telecommunication network.

5.3	Service accessibility performance

5301	service accessibility; service access probability

F:	accessibilité (d'un service)

S:	accesibilidad de un servicio; probabilidad de acceso a un servicio

The probability that a service can be obtained within specified tolerances and other given operating conditions when requested by the user.

5302	mean service access delay

F:	durée moyenne d'accès

S:	retardo medio de acceso a un servicio; demora media de acceso a un servicio

The expectation of the time duration between an initial bid by the user for the acquisition of a service and the instant of time the user has access to the service, the service being obtained within specified tolerances and other given operating conditions.

5303	network accessibility

F:	accessibilité (d'un réseau)

S:	accesibilidad (de una red)

The probability that the user of a service after a request receives the proceed-to-select signal within specified conditions.

Note - The proceed-to-select signal is that signal inviting the user to select the desired destination.

5304	connection accessibility

F:	accessibilité

S:	accesibilidad de una conexión

The probability that a connection can be established within specified tolerances and other given conditions following receipt by the exchange of a valid code.

5305	mean access delay

F:	durée moyenne d'accès

S:	retardo medio de acceso; demora media de acceso

The expectation of the time duration between the first call attempt made by a user of a telecommunication network to reach another user or a service and the instant of time the user reaches the wanted other user or service, within specified tolerances and under given operational conditions.

5306	p-fractile access delay

F:	quantile-p de la durée d'accès

S:	cuantil-p del retardo de acceso; cuantil-p de la demora de acceso

The p-fractile value of the duration between the first call attempt made by a user of a telecommunication network to reach another user or a service and the instant of time the user reaches the wanted other user or service, within specified tolerances and under given operational conditions.

5307	accessibility of a connection to be established

F:	accessibilité d'une communication à établir

S:	accesibilidad de una conexión por establecer

The probability that a switched connection can be established, within specified transmission tolerances, to the correct destination, within a given time interval, when requested by the user.

Note 1 - For user-originated calls, it could express the probability of a successful call establishment on the first attempt. For operator-handled calls, it could represent the probability of having a satisfactory connection established within a given time duration.

Note 2 - In general, the tolerances should correspond to a level of transmission performance which makes the connection unsatisfactory for

service such that, for example, a substantial percentage of users would abandon the connection.

5308	unacceptable transmission probability

F:	probabilité d'une transmission inacceptable

S:	probabilidad de transmisión inaceptable

The probability of a connection being established with an unacceptable speech path transmission quality.

5309	no tone probability

F:	probabilité de non tonalité

S:	probabilidad de ausencia de tono

The probability of a call attempt encountering no tone following receipt of a valid code by the exchange.

5310	misrouting probability

F:	probabilité d'acheminement errone

S:	probabilidad de encaminamiento erróneo

The probability of a call attempt being misrouted following receipt by the exchange of a valid code.

5.4	Service retainability performance

5401	service retainability

F:	continuabilité (d'un service)

S:	retenibilidad (de un servicio)

The probability that a service, once obtained, will continue to be provided under given conditions for a given time duration.

5402	connection retainability

F:	continuabilité (d'une chaîne de connexion)

S:	retenibilidad (de una conexión)

The probability that a connection, once obtained, will continue to be provided for a communication under given conditions for a given time duration.

5403	retainability of an established connection

F:	continuabilité d'une communication établie

S:	retenibilidad de una conexión establecida

The probability that a switched connection, once established, will operate within specified transmission tolerances without interruption for a given time interval.

5404	premature release probability; cut-off call probability

F:	probabilité de libération prématurée

S:	probabilidad de liberación prematura; probabilidad de corte de una llamada

The probability that an established connection will be released for a reason other than intentionally by any of the parties involved in the call.

5405	release failure probability

F:	probabilité de non-libération

S:	probabilidad de fallo de liberación

The probability that the required release of a connection will not take place.

5.5	Serveability performance

5501	probability of successful service completion

F:	probabilité d'exécution correcte du service

S:	probabilidad de prestación satisfactoria de un servicio

The probability that a connection can be established, under satisfactory operating conditions, and retained for a given time interval.

5.6	Transmission performance

5601	bit error ratio (BER)

F:	taux d'erreur sur les bits (TEB)

S:	tasa de errores en los bits; tasa de error en los bits (TEB)

The ratio of the number of bit errors to the total number of bits transmitted in a given time interval.

5602	error free seconds (EFS)

F:	secondes sans erreur (SSE)

S:	segundos sin error (SSE)

The ratio of the number of one-second intervals during which no bits are received in error to the total number of one-second intervals in the time interval.

Note 1 - The length of the time interval needs to be specified.

Note 2 - This ratio is usually expressed as a percentage.

6	Common concepts

The following concepts are used in the definitions of this Recommendation. Others used, such as probability, measure, up state, disabled state, time duration, user and connection may be found in Recommendation E.600 and in Supplement No. 6.

6001	service

F:	service

S:	servicio

A set of functions offered to a user by an organization.

6002	item; entity

F:	entité; individu

S:	elemento; entidad; ítem

Any part, device, subsystem, functional unit, equipment or system that can be individually considered.

Note 1 - An item may consist of hardware, software or both, and may also include people, e.g. operators in a telephone operator system.

Note 2 - In French, the term entité replaces the term dispositif previously used in this meaning, because the term dispositif is also the common equivalent for the English term "device".

Note 3 - In French, the term individu is used mainly in statistics.

ANNEX A

(to Recommendation E.800)

Alphabetical list of definitions contained in this Recommendation

5307	accessibility of a connection to be established

5102	billing error probability

5106	billing integrity (probability)

5601	bit error ratio

5204	call abandonment probability

3203	capability

5304	connection accessibility

4101	break (of service)

5402	connection retainability

5404	cut-off call probability

5202	dialling mistake probability

3205	effectiveness (performance)

6002	entity

5602	error free seconds (EFS)

5103	incorrect charging or accounting probability

4103	interruption duration

4101	interruption

6002	item

5305	mean access delay

4105	mean interruption duration

5302	mean service access delay

5101	mean service provisioning time

4104	mean time between interruptions

5310	misrouting probability

5303	network accessibility

3201	network performance5

309	no tone probability

5105	overcharging probability

5306	p-fractile access delay

5404	premature release probability

5501	probability of successful service completion

3204	propagation performance

3101	quality of service

5405	release failure probability

5403	retainability of an established connection

3102	serveability performance

6001	service

5301	service access probability

5301	service accessibility

3103	service accessibility performance

3107	service integrity

3106	service operability performance

5401	service retainability

3104	service retainability performance

3105	service support performance

5203	service user abandonment probability

5201	service user mistake probability

4102	time between interruptions

3202	trafficability performance

3108	transmission performance

5308	unacceptable transmission probability

5104	undercharging probability